Field of the Invention
The present invention relates to a sheet conveyance technique, and more particularly, to a purge technique.
Description of the Related Art
An image forming apparatus such as a printer or a copying machine normally forms an image on each sheet while successively conveying sheets along one path. In a case where a defect such as a paper jam (a jam) or image quality degradation happens to a sheet moving in the path, the image forming apparatus normally suspends processing, and forcibly keeps the other moving sheets at appropriate locations in the path. To cause the image forming apparatus to resume the processing, all the sheets on which any processing can no longer be performed among the suspended sheets need to be removed from the path. However, leaving this removal operation to a user imposes a heavy burden on the user.
There is a type of conventional image forming apparatus that automatically removes sheets staying in the path when processing is suspended to free the user from the burden (see JP 2015-036741 A, JP 2014-164011 A, JP 2013-235137 A, and JP 2008-052125 A, for example). This removal operation is called “purge”. Sheets as purge targets are purged and moved to a different discharge destination from the original discharge destination. The different discharge destination, or a purge destination, is normally a tray or a cassette or the like provided for purges. Furthermore, in a large-sized apparatus such as a projection printer (PP) or larger, two or more discharge destinations are already provided at appropriate locations in the path. One discharge destination selected beforehand from among the discharge destinations by a user, or the discharge destination that is located on the upstream side of the site of occurrence of a jam and is the closest to the site of occurrence of the jam among the discharge destinations is used as the purge destination (see JP 2014-164011 A, for example).
Normally, a conventional image forming apparatus automatically performs a purge every time a defect occurs in sheet conveyance. However, when such an apparatus is made to print a confidential document, such a purge is accompanied by a risk of information leakage. In reality, a user sometimes fails to remove the purged sheets, since the purge destination differs from the original discharge destination. Particularly, in a PP, there are two or more discharge destinations, and there is a high risk of a user failing to check which discharge destination is selected as the purge destination. As a result, a sheet left at the purge destination might mix with other printed materials, and be exposed to a third party.